Surgically implantable total ankle prosthesis

ABSTRACT

An implantable total ankle prosthesis consists of an upper portion formed of highly polished metal having a stem which is firmly attached to a correspondingly shaped slot formed in the tibia, and a lower portion formed of ultra-high density polyethelyne and having a shank shaped to be sunk into a cavity formed in the surface of the body of the talus. The confronting surfaces of the upper and lower portions are both convex, thereby to provide a bi-plane sliding joint having minimal friction and allowing simultaneous rotational movement. The prosthesis is implantable through an anterior or anterior-medial incision, this approach leaving the ligaments on the lateral and medial side of the ankle joint essentially undisturbed so as to preserve the normal medial-lateral stability of the articulation.

United States Patent 1 i [111 3,886,599

Schlein June 3, 1975 SURGICALLY IMPLANTABLE TOTAL Primary ExaminerRonald L. Frinks ANKLE PROSTHESIS Attorney, Agent, or FirmSpencer E. Olson [75] Inventor: Allen P. Schlein, Stratford, Conn. [73] Assignee: Louis Charles Schlein, Union, NJ. [57] ABSTRACT An implantable total ankle prosthesis consists of an [22] Filed: July 1974 upper portion formed of highly polished metal having [21] Appl. No.: 491,754 a stem which is firmly attached to a correspondingly shaped slot formed in the tibia, and a lower portion formed of ultra-high density polyethelyne and having a shank shaped -to be sunk into a cavity formed in the surface of the body of the talus. The confronting surfaces of the upper and lower portions are both convex, thereby to provide a bi-plane sliding joint having mini- [56] References Cited mal friction and allowing simultaneous rotational UNITED STATES AT movement. The prosthesis is implantable through an 3 521 302 7/1970 anterior or anterior-medial incision, this approach I 3,715,763 2/1973 leaving the ligaments on the lateral and medial side of 3,774,244 1/19 the ankle joint essentially undisturbed so as to pre- 3,839,742 10/ 1974 serve the normal medial-lateral stability of the articulation.

[52] US. Cl. 3/1; 128/92 C [51] Int. Cl. A61f l/24 [58] Field of Search..... 3/1; 128/92 C, 92 CA, 92 R 6 Claims, 6 Drawing Figures SURGICALLY IMPLANTABLE TOTAL ANKLE PROSTHESIS BACKGROUND OF THE INVENTION Research workers have for many years attempted to find ways to lessen the disability for the patient suffering from degenerative or post traumatic arthritis of the ankle joint, as well as avascular necrosis of the talus. Although the development of non-reactive metallic implants has made it possible to replace other joints of the human body, such as the elbow and the knee, until very recently the usual procedure for the treatment of the ankle joint was to obliterate the joint by fusion, which, of course, rendersthe ankle stiff and generally immobile, or by surgical removal of the damaged portions of the ankle joint and provision of a suitable ankle brace to give the patient some mobility.

The first reported use of a total ankle prosthesis known to applicant was by Buchholz in 1969 who implanted a device across the tibial-talar joint which consisted of a plastic insert in the tibia which engages a metal insert in the talus. The prosthesis, known as the St. Georg-Buchholz Total Ankle, is currently manufactured by the Waldemar Link Company in Hamburg, Germany and is distributed in the United States and Canada by Richards Manufacturing Company, Inc., Memphis, Tenn. In this device, the contact between the two inserts is convex-to-concave, which allows sliding contact in the anterior-posterior plane only and does not allow rotation of the ankle about a vertical axis, which tends to cause the inserts to loosen and require replacement. Moreover, insertion of this prosthesis requires osteotomy of the fibula, as well as temporary placement of a screw in the medial malleolus. This additional surgery, involving cracking of both sides of the ankle, tends to lengthen the period of rehabilitation, particularly in older patients.

G. Lord and J. H. Marote reported in 1971 in Journal of Orthopedics of the Hospital R. Poincare that arthoplasty of the ankle joint could be performed by total resection of the talus, fixation in the tibia of a metallic prosthesis, resembling that used in the hip, to engage a high density polyethylene bearing device placed in the calcaneus. The metallic portion is a relatively large spherical knob which forms a ball-and-socket type of joint with the bearing device, again a convex-tconcave contact, which permits some degree of rotation of the ankle about a vertical axis but no sliding motion. Insertion of the relatively large parts requires removal of the whole talus, tending to weaken the bearing structure. A ball-and-socket joint proposed by Richard Smith of San Diego, Calif. is somewhat smaller than that described by Lord and Marote, but it, too, does not allow for sliding motion in the anteriorposterior plane. Absence of such sliding motion, which is presentin the healthy human ankle joint, can be expected to cause shearing and early destruction of the digh density plastic utilized as one of the bearing memers.

SUMMARY OF THE INVENTION The primary object of the present invention is to provide an improved implantable total ankle prosthesis having a bi-plane sliding motion which also allows dissipation of rotary forces and exhibiting minimal frictional forces. A more specific object is to provide a total ankle prosthesis which is relatively simple and inexpensive to fabricate, which is fully compatible with human body tissue, and which may be implanted with a minimum of disturbance of the ligaments that provide the normal medial-lateral stability of the articulation. These and other objects are accomplished in a prosthesis consisting of a sliding joint having a convex-toconvex bearing surface provided by an upper portion fabricated of polished Vitallium, a non-reactive alloy of chrome, nickel and cobalt, formed to have a T-shaped stem adapted for insertion in a correspondingly shaped slot formed in the tibia to there be held in place by a suitable cement. The lower portion of the joint is formed of ultra-high density polyethylene and has a shank shaped to be sunk into a cavity either milled or drilled in the surface of the body of the talus. Its bearing surface is also convex in shape, and in plan is trapezoidal in shape, being somewhat narrower at its posterior edge than at its anterior edge. The confronting convex bearing surfaces of the upper and lower portions of the joint provides a line contact which allows them to slide in bi-plane fashion relative to each other, and also allows rotation of the ankle about a vertical axis. In other words, one portion of the joint can roll on the other, or can slide relative to the other so that articulation of the joint portions closely simulates human ankle joint action. The low-friction metal-topolyethylene bearing substantially eliminates the possibility of reactive foreign particles being dispersed into the surrounding tissue.

DESCRIPTION OF THE DRAWINGS Other objects, features and advantages of the invention, and a better understanding of its construction and operation will be had from the following detailed description, taken in conjunction with the accompanying drawings, in which:

FIG. 1 is an isometric view, greatly enlarged, of the ankle joint prosthesis according to the invention;

FIG. 1A is a front elevation view of the upper portion of the prosthetic joint;

FIG. 1B is a plan view of the upper surface of the lower portion of the joint;

FIG. 1C is a side elevation view of the lower portion;

FIG. 1D is a plan view of the underside of the lower portion; and

FIG. 2 is an anterior cutaway view of the human ankle showing the prosthesis in place.

DESCRIPTION OF THE PREFERRED EMBODIMENT The prosthesis according to the invention, which is shown greatly enlarged in the drawings, consists of two cooperating portions having confronting bearing surfaces, an upper portion 10 for attachment to the tibia, and a lower portion 12 to be secured to the talus. The upper portion is formed, as by casting, of a nonreactive metal, preferably a chrome-nickel-cobalt alloy known as Vitallium, and consists of a generally rectangularly shaped block 14, typically 32mm. long and 18mm. wide and 8mm. high. The under surface of the block is of convex shape. Integrally joined to and extending upwardly from approximately the geometric center of the rectangular upper surface of the block 14 is a T-shaped stem 16 of square cross-section, typically 6mm. by 6mm, having an overall length of about 15mm. In use, the T-shaped stem is inserted in a correspondingly shaped slot formed in the tibia and held in place by methylmathacrylate cement. The T-shape of the stem not only holds the element in the tibia, but also resists rotational forces to insure continued proper alignment of the upper portion with the lower portion with which it co-acts. As further insurance against displacement of the metallic implant relative to the tibia a groove 16a is formed in the upper surface and perpendicular to the axis of the cross-bar of the T, and depressions are formed in at least two of the vertical surfaces of the stem, one of which is visible at 16b in FIG. 1.

The lower portion 12 of the joint is formed, as by machining, of ultra-high density polyethylene and has a convex surface 18 which, when the prosthesis is in use, confronts and engages the convex surface of the upper portion 10. The radius of curvature of the surface 10 is typically 25mm. and is generally trapezoidal in shape, its posterior dimension 18a being somewhat smaller than its anterior dimension 18b. Typically, the front-toback dimension of the surface is 22 mm., and its nominal width is mm. As shown in FIG. 1C, the plastic component is squared off at its anterior and posterior edges, and on the underside is formed to have a planar surface 18C from which depends an integral shank 18, approximately 4.8mm long and of circular crosssection. The shank has a reverse taper to resist pullout, the maximum diameter being typically 16mm, and is formed with cross slots 18s to prevent rotation. When implanted, the shank 18d is sunk into a circular cavity drilled in the surface of the body of the talus, with the surface 18c engaging the surface of the talus surrounding the cavity. The lower portion 12 is firmly secured in the talar cavity by a suitable methylmathacrylate cement, the gripping power of which is increased by the reverse taper and the cross slots.

Without going into the full details of the operation procedure, the manner in which the prosthesis is implanted will now be generally described with reference to FIG. 2. An anterior or anterior-medial approach to the ankle joint is preferred because an incision at either of these locations preserves the medial and anterior talo-fibular ligaments on the lateral and medial sides of the ankle joint and so preserves the normal mediallateral stability of the articulation. Depending on the nature of the damage to the cartilage separating the tibia and the talus, the remaining cartilage of the tibia and approximately one quarter inch of the bone are resected. The T-shaped stem is then placed against the tibia at the intended location of the implant and the location marked. Using appropriate chisels, gouges and burring tools, a T-shaped slot is resected, the slot being slightly larger than the T-shaped stem so as to permit the metallic tibial component to be placed in position on the under surface of the resected tibia.

The next step involves resection of from one-fourth inch to three-eighths inch of the superior surface of the talus. Thereafter the surface of the resected talus is marked or scribed to indicate the outline of the plastic member at its desired location, together with the location of the shank 18d relative to the outline. Then a circular cavity of diameter slightly larger than the diameter of the shank is drilled and/or reamed into the body of the talus to a depth slightly greater than the length of the shank.

After the two components have been trail fitted for parallelism and are observed to slide under direct vision, they are then permanently cemented into place with methylmathacrylate cement.

The wound is then closed in layers and a suction drain is usually left in place for 24 to 48 hours. External immobilation of the ankle joint is utilized for a period of fourteen to twenty-one days before the patient is allowed to bear any weight on the new articulation.

It will be apparent from the foregoing that applicant has provided a total ankle prosthesis which by reason of its small size permits implantation with a minimum of disturbance of the ligaments of the ankle, is free of external protuberances that could cause irritation of surrounding tissue, has low friction, and does not have metal-to-metal contacts which can cause dispersion of reactive metal particles. Its convex-to-convex contact provides a line contact which can slide in both the anterior-posterior plane and in the plane perpendicular thereto, and which also allows rotation about a vertical axis, thus closely simulating the action of the normal human ankle joint. While there is disclosed what is now considered to be a preferred embodiment, many modifications and variations therein will be readily apparent to those skilled in the art. For example, the dimensions of the parts are subject to considerable variation without losing the advantages of the invention; specifically, the convexity of the confronting surfaces may be different than indicated, including reduction of the convexity of the talar member to almost flat. All such modifications are within the intended scope of the invention as defined by the following claims.

I claim:

1. Prosthesis for total replacement of the ankle joint of humans comprising,

first and second bearing members each having a convex surface and adapted to engage each other along a line contact, said first bearing member being formed of a metal alloy which is essentially non-reactive with body tissue and having a stern adapted to be received in a cavity formed in the tibia, and

said second bearing member being formed of high density plastic material and including an integral shank adapted to be received in a cavity formed in the surface of the head of the talus.

2. Prosthesis in accordance with claim 1 wherein said first bearing member comprises a generally rectangular block of said metal alloy, one surface of which has a predetermined radius of curvature defining its convex bearing surface, and wherein said stem is of T-shape and extends upwardly from the surface of the block opposite the convex surface.

3. Prosthesis in accordance with claim 2, wherein the convex surface of said second bearing member is of trapezoidal shape, with the posterior dimension being narrower than the anterior dimension.

4. Prosthesis in accordance with claim 3, wherein the shank on said second bearing member depends from the surface thereof opposite the convex surface and is of circular cross-section.

5. Prosthesis in accordance with claim 2, wherein said T-shaped stem has at least one groove formed therein for increasing the holding power of the cement with which said bearing member is secured to the tibia.

6. Prosthesis in accordance with claim 4, wherein the shank of said second bearing member has a reverse taper and has at least one groove formed in the free end thereof to increase the holding strength of the cement employed to secure said second bearing member in the cavity formed in the talus. 

1. Prosthesis for total replacement of the ankle joint of humans comprising, first and second bearing members each having a convex surface and adapted to engage each other along a line contact, said first bearing member being formed of a metal alloy which is essentially non-reactive with body tissue and having a stem adapted to be received in a cavity formed in the tibia, and said second bearing member being formed of high density plastic material and including an integral shank adapted to be received in a cavity formed in the surface of the head of the talus.
 1. Prosthesis for total replacement of the ankle joint of humans comprising, first and second bearing members each having a convex surface and adapted to engage each other along a line contact, said first bearing member being formed of a metal alloy which is essentially non-reactive with body tissue and having a stem adapted to be received in a cavity formed in the tibia, and said second bearing member being formed of high density plastic material and including an integral shank adapted to be received in a cavity formed in the surface of the head of the talus.
 2. Prosthesis in accordance with claim 1 wherein said first bearing member comprises a generally rectangular block of said metal alloy, one surface of which has a predetermined radius of curvature defining its convex bearing surface, and wherein said stem is of T-shape and extends upwardly from the surface of the block opposite the convex surface.
 3. Prosthesis in accordance with claim 2, wherein the convex surface of said second bearing member is of trapezoidal shape, with the posterior dimension being narrower than the anterior dimension.
 4. Prosthesis in accordance with claim 3, wherein the shank on said second bearing member depends from the surface thereof opposite the convex surface and is of circular cross-section.
 5. Prosthesis in accordance with claim 2, wherein said T-shaped stem has at least one groove formed therein for increasing the holding power of the cement with which said bearing member is secured to the tibia. 